我们的冰与火晕：银河系晕中的强烈运动学不对称性
Our Halo of Ice and Fire: Strong Kinematic Asymmetries in the Galactic Halo
AI总结：
本研究利用H3巡天绘制银河系晕恒星运动学，发现其存在强烈不对称性，吸积与原位星族运动特征差异显著，揭示银晕非球形异质特性，为准确约束银河系引力场及总质量提供新路径。
摘要：
恒星晕的运动学特征为揭示银河系的组装历史与质量分布提供了重要线索。本研究利用H3巡天（H3 Survey）绘制了整个银河系晕中恒星的运动学分布。我们发现其分布十分复杂，既打破了绕Z轴的方位角对称性，也打破了关于银道面的镜像对称性。这种不对称性表现为径向速度弥散σ_r的大幅波动，范围从低至70 km s⁻¹的“冷”状态到高达160 km s⁻¹的“热”状态。我们通过恒星化学组成区分了晕中的吸积恒星与原位恒星，发现吸积星族的σ_r更高且轨道呈径向偏置，而原位星族的σ_r更低且轨道各向同性。因此，银河系晕的运动学具有高度异质性，无法用球形或轴对称模型很好地近似。我们测量了银心距10-80 kpc范围内σ_r和各向异性参数β的径向剖面，发现已有文献中的结果差异源于银晕的非球形几何结构与异质性。探究强不对称的σ_r和β对平衡模型的影响，是准确约束银河系引力场（包括其总质量）的可行方向。
英文摘要：
The kinematics of the stellar halo hold important clues to the assembly history and mass distribution of the Galaxy. In this study, we map the kinematics of stars across the Galactic halo with the H3 Survey. We find a complex distribution that breaks both azimuthal symmetry about the $Z$-axis and mirror symmetry about the Galactic plane. This asymmetry manifests as large variations in the radial velocity dispersion $σ_r$ from as ``cold'' as 70 $\text{km}\text{ s}^{-1}$ to as ``hot'' as 160 $\text{km}\text{ s}^{-1}$. We use stellar chemistry to distinguish accreted stars from in-situ stars in the halo, and find that the accreted population has higher $σ_r$ and radially biased orbits, while the in-situ population has lower $σ_r$ and isotropic orbits. As a result, the Galactic halo kinematics are highly heterogeneous and poorly approximated as being spherical or axisymmetric. We measure radial profiles of $σ_r$ and the anisotropy parameter $β$ over Galactocentric radii $10-80\text{ kpc}$, and find that discrepancies in the literature are due to the nonspherical geometry and heterogeneous nature of the halo. Investigating the effect of strongly asymmetric $σ_r$ and $β$ on equilibrium models is a path forward to accurately constraining the Galactic gravitational field, including its total mass.
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